#define _CRT_SECURE_NO_WARNINGS
#include<stdio.h>
int main()
{
	char killer = 'a';
	
	for (; killer <= 'd'; killer++)
	{
		if ((killer != 'a')+(killer == 'c')+(killer == 'd')+(killer != 'd') == 3)
		{
			printf("%c", killer);
		}
	}
	return 0;
}